I have the same problem here. Win 8.
After some indeterminate amount of time no more sound will happen on my pc until I reboot. My browser windows lag horrible until I get a message that says shockwave flash has crashed (due to its inability to communicate with my UX2).
Line 6 Monkey at this time reports the ESN: Unknown and Firmware version: Unknown. When I restart my PC, there is a number for the ESN and the Firmware version is 1.02.
Any idea what's wrong? My UX2 has been a big issue for me in the last 4 or 5 years that I've had it. It would be a really great useful little thing if it didn't crash so much, but it was designed forever ago so I'm really not surprised.